Method for measuring the flow of fluids

ABSTRACT

The disclosed method of measuring the flow of a fluid with a porous particulate ceramic tracer and an optical instrument is characterized in that spherical particles having diameters in the range of 0.5 to 150 μm are used as the tracer. Inasmuch as the tracer particles for flow measurement are spherical, the sectional area of scattered light to be detected by an optical sensor means is constant regardless of the orientation of particles. Furthermore, spherical particles have no surface irregularities that might cause concatenation so that individual particles are not agglomerated in tracking a fluid flow, thus contributing to improved measurement accuracy.

TECHNICAL FIELD

[0001] The present invention relates to a method for measuring the flowof fluids, herein after referred to as “flow measurement”. It should,however, be understood that the term “flowmeasurement” as usedthroughout this specification means not only a measurement of the flowvelocity of a gas, such as air, fuel gas, etc., or a liquid, such aswater, liquefied gas, etc., but also a topological visualization of thedistribution of such gas or liquid.

BACKGROUND OF THE INVENTION

[0002] Prior Art

[0003] The particles heretofore used as tracer particles in optical flowmeasurements are porous particles made of SiO₂, TiO₂, SiC or the likewhich are obtainable by a coprecipitation process or from a naturalmaterial such as the mineral ore. These particles generally have a meanparticle diameter of about 0.5 to 150 μm.

[0004] In a measurement of the flow velocity using a laser device suchas a laser Doppler velocimeter, a phase Doppler velocimeter or the like,tracer particles somewhere between 0.5 and 10, μm in mean diameter, inparticular, have so far been employed.

[0005] In technologies involving a visualization of a flowing fluid byphotographing the distribution of tracer particles in the fluid with theaid of an instantaneous, powerful light source, such as a flashlight ora pulse laser, and a determination of the flow pattern from theresulting picture, particles somewhere between about 5 μm and about 150μm in mean diameter are generally employed.

[0006] Electron microphotographs of the representative tracer particleswhich are conventionally employed are presented in FIGS. 3 through 14;viz. white carbon in FIGS. 3 and 4, TiO₂ in FIGS. 5 and 6, talc in FIGS.7 and 8, TiO₂-talc in FIGS. 9 and 10, particles from kanto loam, andwhite alumina in FIGS. 13 and 14.

[0007] However, as apparent from these microphotographs, theconventional tracer particles have the following drawbacks, 1) through5), which amplify the measurement error.

[0008] 1) Because the tracer particles are morphologically not uniform,the sectional area of scattered light to be detected varies according tothe real-time orientation of each particle.

[0009] 2) Because the particle size distribution is broad and thesectional area of light scattering varies with different individualparticles, the comparatively large particles scatter light in two ormore fringe at a time.

[0010] 3) Because the apparent specific gravity of the particulatetracer differs markedly from that of the fluid to be measured, theparticles do not faithfully follow the on-going flow of the fluid.

[0011] 4) Because the particle size distribution is broad and theapparent specific gravity also has a distribution, the particles followthe fluid flow with varying efficiencies to prevent accuratequantitation of the flow measurement.

[0012] 5) Because the surface of the particle is irregular, theindividual particles tend to be concatenated with each other to increasethe effective particle size.

[0013] The technique used generally for launching tracer particles intoa fluid comprises either extruding tracer particles from a screw feederand driving them into the body of the fluid with the aid of an aircurrent or suspending tracer particles in a solvent and ejecting thesuspension in a mist form using an ultra-sonic humidifier. In any of theabove methods, the rate of feed of the tracer particles is not constantso that the accuracy of flow measurement is inevitably sacrificed.

OBJECTS OF THE INVENTION

[0014] It is the object of the present invention to overcome theabove-mentioned drawbacks and provide a method of flow measurement withimproved accuracy.

SUMMARY OF THE INVENTION

[0015] The method of flow measurement according to the inventioncomprises measuring the flow of a fluid using an optical instrument anda porous particulate ceramic tracer, the diameter of which is 0.5 to 150μm.

[0016] In another aspect, the method of flow measurement according tothe invention comprises feeding a non-agglomerating particulate tracerto an optical instrument, such as a laser device, from a measuring wheelparticle feeder.

[0017] The method of flow measurement according to the inventioncomprises measuring the flow of a fluid using an optical instrument anda porous particulate ceramic tracer, said porous particulate ceramictracer consisting of spherical particles having a diameter of 0.5 to 150μm. Particularly in the method of measuring the flow velocity using alaser instrument such as a laser Doppler velocimeter, spherical ceramicparticles having a diameter of 0.5 to 10 μm are preferred from theviewpoint of relation with fringe.. A more satisfactory sphericalparticle diameter range is 1.5 to 2.5 μm. In flow measurement whichinvolves photographing, the use of spherical particles having a diameterof 5 to 150 μm is preferred from the viewpoint of detecting light andflowing the fluid flow. A more satisfactory particle diameter range is30 to 100 μm.

[0018] When the tracer particles for use in flow measurement with anoptical instrument are spherical as in the invention, the sectional areaof scattered light to be detected by a photosensor or the like isconstant regardless of the orientation of particles at the moment ofdetection. Moreover, because such particles have no surfaceirregularities that may cause concatenation, it does not happen that twoor more tracer particles flow as concatenated through the body of thefluid. Therefore, the accuracy of flow measurement is improved.

[0019] Where the fluid to be measured is a gas, said tracer particlesare preferably of hollow structure.

[0020] When the tracer particles are hollow, the specific gravity of theparticles is so low that even if the particle size is not criticallyuniform, they may readily follow the gas flow. Therefore, the accuracyof gas flow measurement is improved. The improved accuracy ofmeasurement afforded by such hollow spherical particles over thatattainable with solid spherical particles is more remarkable when theflow rate of the fluid is high.

[0021] The shell thickness of such hollow spherical particles is not socritical but is preferably in the range of one-third to one-tenth of thediameter of the particle. If the shell thickness is less than one-tenthof the particle diameter, the particles tend to be collapsed in use.Conversely when the shell is thicker than one-third of the particlediameter, the advantage of the hollow structure will not be fullyrealized.

[0022] Where the fluid to be measured is a liquid, said tracer ispreferably a porous particulate ceramic tracer having closed pores witha porosity of not less than 0.1 cm³/g.

[0023] When the tracer particles have closed pores with a porosity ofnot less than 0.1 cm³/g, the specific gravity of the tracer particlescan be changed so as to minimize the differential from the specificgravity of the fluid to be measured, thereby making it easier for theparticles to follow the dynamics of the fluid. In this manner, theaccuracy of flow measurement can be further improved.

[0024] Where the fluid to be measured is a liquid, tracer particlescoated with a metal are used with advantage.

[0025] When such metal-clad porous spherical particles are used for theflow measurement of a liquid, the intensity of reflected light isgreater than-it is the case when bare particles are employed so that theaccuracy of flow measurement is improved. However, since such metal-cladparticles are higher in specific gravity and expensive, they arepreferably used where the conditions of measurement specifically callfor the use of such particles.

[0026] Particularly preferred are metal-clad porous ceramic tracerparticles having closed pores with a porosity of not less than 0.1cm^(3/)g. Application of a metal cladding increases the specific gravityof particles as mentioned above but the adverse effect of increasedspecific gravity can be minimized by using porous ceramic particleshaving closed pores with a porosity of not less than 0.1 cm³/g.

[0027] For application of a metal cladding, any of the electrolessplating, electrolytic plating, CVD, vapor deposition and othertechniques can be utilized but the electroless plating process ispreferred in that a uniform cladding can be easily obtained,

[0028] The cladding metal includes, among others, Ni, Pt, Co, Cr, etc.but nickel is preferred in that a quality cladding can be easilyobtained by electroless plating and that the resultant cladding iscomparatively high in chemical resistance.

[0029] The thickness of the metal cladding is not critical but ispreferably within the range of 0.05 to 5 μm. If the cladding thicknessis less than 0.05 μm, the effect of increased reflectance is hardlyobtained. If the cladding is over 5 μm in thickness, the proportion ofthe metal in the whole particle is too large so that the bulk specificgravity of the tracer is increased.

[0030] The starting material for said particulate tracer or for theceramic part of said metal-clad particulate tracer is not limited invariety only if it is chemically stable. Thus, the starting material canbe selected from among, for example, alkaline earth metal carbonatessuch as calcium carbonate, barium carbonate, etc., alkaline earth metalsilicates such as calcium silicate, magnesium silicate, etc.; and metaloxides such as silica (SiO₂), iron oxide, alumina, copper oxide and soon. Among these materials, SiO₂ is particularly desirable in that it iscommercially available at a low price and resistant to heat. When theheat resistance of the ceramic material is high, particles preparedtherefrom can be effectively used without the risk of breakdown even inhigh-temperature fluids.

[0031] The size distribution of tracer particles is preferably as narrowas possible but when not less than 70% of the particles have diameterswithin the range of ±50% of the mean particle diameter, there isobtained a substantially uniform sectional area of scattered light.Moreover, the kinetics of tracer particles in the fluid body, that is tosay the pattern of following the fluid flow, are then renderedsubstantially uniform.

[0032] The tracer particles of the invention can be applied to themeasurement of fluids flowing at high speeds. Thus, in the conventionalflow measurement using a laser Doppler device, an attempt to increasethe sample data rate (the number of data generated per unit time) byincreasing the flow rate of the fluid and, hence, the number of tracerparticles passing through the fringe per unit time resulted in adecrease in the mean effective data rate, which is a representativeindicator of measurement accuracy, thus making it difficult to achievean accurate measurement of a high-velocity fluid. In accordance with thepresent invention, the mean effective data rate is high even at a highsample data rate so that the method can be effectively applied to themeasurement of fluids flowing at high speeds.

[0033] Furthermore, in the conventional flow measurement, theconcentration of tracer particles cannot be increased over a certainlimit because an increased feed of tracer particles for generating alarger number of data per unit time should adversely affect the meaneffective data rate. However, in the method of the invention, increasingthe rate of feed of tracer particles for increasing the sample data ratedoes not sacrifice the mean effective data rate, with the result thatthe desired measurement can be performed with an increased tracerconcentration.

[0034] The particulate tracer or the ceramic core of the metal-cladparticulate tracer can be easily manufactured at low cost by thereversed micelle technology which provides spherical or hollow sphericalporous tracer particles.

[0035] In this connection, when an aqueous solution of the precursor forthe tracer material is extruded from a porous glass or polymer membranehaving substantially uniform pores in an organic solvent, there can beobtained uniform particles with a narrow size distribution, and suchparticles are well suited for use as the tracer particles or the core ofmetal-clad tracer particles.

[0036] The above-mentioned porous glass or polymer membrane may be anyof the known membranes such as the membrane obtainable by subjectingborosilicate glass to phase separation and washing the product with apickling acid solution, the membrane obtainable by mixing a silica solwith a water-soluble organic polymeric material, subjecting the mixtureto phase separation at polymerization and rinsing the product, and themembrane obtainable by a technology involving irradiation with laserlight to give perforations of substantially uniform diameter.

[0037] The tracer particles can be advantageously fed to the laserinstrument by means of a measuring wheel particle feeder.

[0038] When the tracer particles are fed from the measuring wheelparticle feeder, the particles can be delivered quantitatively so thatthe accuracy of velocity measurement or photographic distributionmeasurement is further improved. Moreover, in the conventional method,for obtaining of the high measurement accuracy, it is essential torecalibrate the instrument after each measurement cycle for minimizingthe measurement error. This operation is eliminated by use of themeasuring wheel particle feeder so that as many more measurements can beperformed within a given time period.

[0039] The construction of the measuring wheel particle feeder and themechanism of feed are described below, referring to FIGS. 15 and 16. Asillustrated, a feeder body 101 is internally provided with a disk 102which is driven by a motor not shown. The top surface of this disk 102is provided with a circumferential groove 103.

[0040] The reference numeral 104 indicates a hopper which is filled witha particulate tracer F. The hopper 104 has a lower portion 104 a whichis tapered towards the discharge end of the hopper and the lowest part104 b thereof is open in the form of an orifice 104 c immediately overthe groove 103, so that the particulate tracer F in the hopper 104 mayflow through the orifice 104 c into the circumferential groove 103.

[0041] The reference numeral 107 indicates a blow nozzle made of platematerial. This blow nozzle 107 is configured as a sector in plan viewand has a recess 109 having a tapered lateral surface 108 in asubstantial center thereof. This recess 109 is centrally provided withan orifice extending in the direction of the thickness for passage oftracer particles (FIG. 16).

[0042] The reference numeral 105 indicates a particle duct which runsthrough a casing 106 of the feeder body 101 and through which the insideof the feeder body 101 is made communicable with the outside thereof.This particle duct 105 is attached to the top of the blow nozzle 107 insuch a manner that its inward end 105 a covers said recess 109 toestablish communication with said particle duct 110.

[0043] The atmospheric pressure within the feeder body 101 is maintainedat a level higher than the external atmospheric pressure. Because ofthis pressure gradient, the air flows into the circumferential groove103 adjacent said blow nozzle 107 at point X beneath the blow nozzle107. The air then flows out through a particle passageway 110, saidrecess 109 and said particle duct 105. The arrowmarks in FIG. 16indicate the flow of air.

[0044] As the particles F are carried by such an air flow, they aresuccessfully metered out from the feeder body 101 into the body of thefluid to be measured.

[0045] In a second aspect, the invention provides a method of flowmeasurement using an optical instrument and a particulate tracermaterial, wherein a non-agglomerating particulate tracer is fed to thelaser or other optical instrument with such a measuring wheel particlefeeder.

[0046] When a non-agglomerating particular tracer material is fed withthe measuring wheel particle feeder for optical instrument, the feedrate can be critically controlled even when the tracer has a largeparticle size distribution and is morphologically divergent as it is thecase with the conventional tracer particles. Thus, the conventionalnon-agglomerating tracer particles are generally large in particle sizeand high in bulk specific gravity so that they cannot faithfully followthe fluid flow but when this measuring wheel particle feeder isemployed, a better tracking performance can be obtained for enhancedmeasuring efficiency under conditions of high flow rate and leastturbulence.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIG. 1 is an electron microphotograph (×2,000) showing theparticles manufactured in accordance with Production Example 1;

[0048]FIG. 2 is an electron microphotograph (×10,000) showing theparticles manufactured in Production Example 1;

[0049]FIG. 3 is an electron microphotograph (×10,000) showing theconventional particles (white carbon);

[0050]FIG. 4 is an electron microphotograph (×50,000) showing the sameconventional particles (white carbon);

[0051]FIG. 5 is an electron microphotograph (×10,000) showing theconventional particles (TiO₂);

[0052]FIG. 6 is an electron microphotograph (×50,000) showing the sameconventional particles (TiO₂);

[0053]FIG. 7 is an electron microphotograph (×1,000) showing theconventional particles (talc);

[0054]FIG. 8 is an electron microphotograph (×10,000) showing the sameconventional particles (talc);

[0055]FIG. 9 is an electron microphotograph (×10,000) showing theconventional particles (TiO₂ -talc);

[0056]FIG. 10 is an electron microphotograph (×50,000) showing the sameconventional particles (TiO₂-talc);

[0057]FIG. 11 is an electron microphotograph (×10,000) showing theconventional particles (source: Kanto loam);

[0058]FIG. 12 is an electron microphotograph (×50,000) showing the sameconventional particles (source: Kanto loam);

[0059]FIG. 13 is an electron microphotograph (×2,000) showing theconventional particles (fused white alumina);

[0060]FIG. 14 is an electron microphotograph (×10,000) showing the sameconventional particles (fused white alumina);

[0061]FIG. 15 is a perspective view showing a measuring wheel particlefeeder;

[0062]FIG. 16 is a partial longitudinal section view showing the blownozzle of the feeder illustrated in FIG. 15;

[0063]FIG. 17 is a schematic view illustrating the manufacturingequipment for tracer particles;

[0064]FIG. 18 is a diagrammatic representation of the particle diameterdistribution of the spherical SiO₂ tracer used in Example 3;

[0065]FIG. 19 is a diagrammatic representation of the particle diameterdistribution of the TiO₂ tracer used in Comparative Example 2;

[0066]FIG. 20 is a diagrammatic representation of the particle diameterdistribution of the SiO₂ tracer used in Comparative Example 3; and

[0067]FIG. 21 is a diagram showing the data obtained in Example 3,Comparative Example 2 and Comparative Example 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] The following examples are further illustrative but notlimitative of the invention.

EXAMPLE 1

[0069] Using a hollow spherical particulate SiO₂ tracer with 70% ofindividual particles having diameters within the range of mean particlediameter=1.5 μm±0.4 μm, the shell thickness of which is one-fifth of thediameter of the particle, the velocity of air within a cylinder wasmeasured using a laser velocimeter under the following conditions andthe relationship between the sample data rate and the mean effectivedata rate was investigated. Thus, for increasing the number of data perunit time (sample data rate) stepwise, the flow rate was increasedstepwise (with the concentration of tracer particles kept constant) toincrease the quantity of particles passing through the inference figureat the flowmeter. Of the resulting data, the percentage of data usefulfor velocity assessment (effective data rate) was determined. (Mean flowrate=ca. 20 m/min.)

[0070] 1. Instrument: Fiber type laser Doppler velocimeter (FLDV)

[0071] (cf. Ikeda, Y., Hikosaka, M., Ohira, T., and Nakajima, T.,Scavenging Flow Measurements in a Fired Two-Stroke Engine by FLDV.,1991. SAE Paper No. 910, p.670)

[0072] (Specification)

[0073] Laser: He-Ne laser

[0074] Laser power: 8 mW×2

[0075] Lens diameter: 55 mm

[0076] 2. Measuring conditions:

[0077] Center frequency: 20 MHz

[0078] Band width: ±16 MHz

[0079] Effective sample number: 5,000

[0080] Signal gain: 24 dB

[0081] Photomultiplier voltage: 760 V

[0082] The results are shown in Table 1.

[0083] [The mean effective data rate was determined with Dantec's burstsignal analyzer. When the symmetry of scatter signals is disturbed, thepeak frequency value after Fourier transformation is depressed.Therefore, only the signals with a frequency peak/reference frequencypeak ratio over a given value were regarded as valid data. In otherwords, the data lacking in signal symmetry were invalidated.] TABLE 1Sample data rate (Hz) Mean effective data rate (%)   300 82   600 80  900 75 1,200 70 1,500 73 1,800 75

[0084] It will be apparent from Table 1 that increasing the sample datarate does not result in any appreciable decreases in the mean effectivedata rate which is a representative indicator of measurement accuracy,indicating that the tracer particles of the invention are fullyeffective for the measurement of high-velocity fluids.

EXAMPLE 2

[0085] The same measurement as Example 1 was performed using a hollowspherical particulate SiO₂ tracer with 90% of individual particleshaving diameters within the range of 1 to 5 μm (the shell thickness wasone-fifth of the diameter of the particle). The results are shown inTable 2. TABLE 2 Sample data rate (Hz) Mean effective data rate (%)  300 80   600 79   900 55 1,200 60 1,500 65 1,800 57

[0086] It will be seen from Table 2 that although the mean effectivedata rates are not as high as those obtained in Example 1 because of thebroader tracer particle size distribution, there are obtained stableeffective data rates even at high sample data rates.

COMPARATIVE EXAMPLE 1

[0087] The same experiment as Example 1 was performed using a wetprocess white carbon, shown in FIGS. 3 and 4, which is a representativeprior art tracer (mean primary particle diameter 0.2 μm, meanagglomerated particle diameter (effective particle diameter) 6 μm;NIPSIL SS-50F, manufactured by Nippon Silica Industry Co., Ltd.). Theresults are shown in Table 3. TABLE 3 Sample data rate (Hz) Meaneffective data rate (%)   300 53   600 63   900 20 1,200 15 1,500 121,800  5

[0088] It will bee apparent from Table 3 that the mean effective datarates are invariably lower than the rates obtained in Examples 1 and 2,with extremely low rates found at high sample data rates.

[0089] It is predictable that the use of the prior art tracer particlesshown in FIGS. 5 through 14 will also yield results similar to thosedescribed above for white carbon.

EXAMPLE 3 AND COMPARATIVE EXAMPLES 2 AND 3

[0090] The velocity of a fluid flowing through an acrylic resin pipewith an internal diameter of 100 mm was determined using: a sphericalparticulate SiO₂ tracer having the particle diameter distribution ofFIG. 18 (Example 3; FIGS. 1 and 2), a particulate TiO₂ tracer having theparticle diameter distribution of FIG. 19 (Comparative Example 2; FIGS.5 and 6) and a particulate SiO₂ tracer having the particle diameterdistribution of FIG. 20 (Comparative Example 3; FIGS. 3 and 4). Fordeterminations, the same fiber type laser Doppler velocimeter (FLDV) asused in Example 1 was employed. A measuring wheel particle feeder(MSF-F, Liquid Gas Co., Ltd.) was used to supply said sphericalparticulate SiO₂ particle and a fluidize bed feeder (Durst et al., 1976)was used to supply said conventional TiO₂ and SiO₂ particles.

[0091] In each determination, the sample data rate was varied bychanging the concentration of tracer particles. The same averagemeasuring speed and root mean square velocity (r.m.s.v.), 122 m/s and3.5 m/s, respectively, were used for the three tracers.

[0092] The relationship between sample data rate and effective data rateis diagrammatically shown in FIG. 21.

[0093] It will be apparent from FIG. 21 that, in accordance with thepresent invention, the effective data rate is not decreased even if thenumber of data per unit time is increased by increasing the feed rate ofparticles.

PRODUCTION EXAMPLE 1

[0094] The following example is intended to illustrate the production oftracer particles by the reversed micelle method.

[0095] A 10 μm-thick polyimide film was irradiated with a KrF excimerlaser (wavelength 251 nm) to provide perforations sized 2.0 μm. Thisperforated polymer film was mounted in an emulsification deviceillustrated in FIG. 17 and an aqueous solution of the tracer precursorsubstance was fed under pressure into an organic solution with a syringepump. The feeding rate was 1 g/cm² and the temperature was 25° C.

[0096] The construction of the device shown in FIG. 17 is summarizedbelow. The reference numeral 10 indicates a volumetric syringe pump 10.The polymer membrane, indicated by 12, is mounted in the forward portionof the volumetric syringe pump. The reference numeral 14 indicates ascreen for supporting said polymer membrane. Indicated by the numeral 16is a cylindrical reactor which is communicating with said syringe pump10. The reference numeral 20 indicates a feed pipe for feeding anorganic solvent 25 from a solvent beaker 24 to said reactor 16 through ametering pump 22. Now, an aqueous solution 11 of the tracer particleprecusor substance is quantitatively injected into the organic solvent25 within the reactor 16 by said syringe pump 10. After formation of alarge number of emulsion particles, the organic solvent is returned fromthe reactor 16 to the solvent beaker 24 via a withdrawal pipe 26.

[0097] In the example, a hexane solution of polyoxyethylene(20)-sorbitan trioleate (20 g/l) was used as the organic solvent.

[0098] As to the aqueous solution, a solution prepared by adding 1.0 molof tetraethoxysilane, 2.2 mol of methanol, 1.0 mol ofN,N-dimethylformamide and 4×10⁻⁴ mols of ammonia to 10 mols of water wasemployed.

[0099] After emulsification at 5° C., the slurry was refluxed for 30hours and the resulting emulsion particles (sol) in the organic acidwere precipitated by gelation. The precipitate was dried and heated at800° C. to give a silica (SiO₂) tracer uniform in particle diameter. Thesilica tracer particles thus obtained were spherical particles, 70% ofwhich had diameters in the range of mean diameter=2.5±0.7 μm (FIGS. 1and 2).

EXAMPLE 4

[0100] For comparing the measuring accuracy obtainable with sphericaltracer particles with that obtainable with hollow spherical tracerparticles, the same experiment as Example 1 was performed using thesolid spherical particles prepared in Production Example 1, that is theparticles with 70% having diameters within the range of mean=2.5±0.7 μm.The results are shown in Table 4. TABLE 4 Sample data rate (Hz) Meaneffective data rate (%)   300 81   600 80   900 74 1,200 73 1,500 631,800 65

[0101] Comparison of Table 4 with Table 1 indicates that both at lowvelocity (low sample data rate) and high velocity (high sample datarate), high measurement accuracy values are obtained and thatparticularly at high velocity, the hollow spherical tracer particlesyield a higher measurement accuracy than the solid spherical tracerparticles, even when the minor difference in particle size is taken intoconsideration.

EXAMPLE 5 AND COMPARATIVE EXAMPLE 4

[0102] Using the conventional particulate TiO₂ tracer for fluidvisualization having a mean particle diameter of 5 μm and a particlespecific gravity of 6 g/cm³ (Comparative Example 4) and a porousspherical particulate SiO₂ tracer having a mean particle diameter of 30μm and a particle specific gravity of about 1 g/cm³ which issubstantially comparable to the first-mentioned tracer in average fluidtracking performance (Example 5, 72% within the range of mean particlediameter±50%), a fluid visualization test was performed by thephotographing method using a flash lamp as the light source.

[0103] As a result, the mean reflection light quantity per particle wasabout 20 times the value of the conventional tracer.

[0104] In terms of the width of spread of particles in the laminar flowregion, the porous spherical particles showed values about 0.8 to 0.5times the values of the conventional particles.

[0105] It is easy to see that, with the average fluid-trackingperformance being fixed, the larger the reflection light quantity, i.e.the signal quantity, and the narrower the spread of tracer particles inthe laminar flow region, the higher is the measurement accuracy.

[0106] It is easily predictable that similar results will be obtainedwhen the conventional tracer particles illustrated in FIGS. 5 through 14are used in lieu of the above tracer particles of Comparative Example 4.

EXAMPLE 6 AND COMPARATIVE EXAMPLE 5

[0107] The same visualization test as above was performed using, insteadof the porous spherical particulate SiO₂ tracer with a mean particlediameter of 30 μm, a porous spherical particulate SiO₂ tracer with amean particle diameter of 100 μm (Example 6; 72% of particles within therange of mean±50%) and a conventional particulate TiO₂ tracer for fluidvisualization which is comparable to the first-mentioned tracer in fluidtracking performance (Comparative Example 5).

[0108] Like the tracer of Example 5, the porous spherical SiO₂ tracerhaving a mean particle diameter of 100 μm was superior to theconventional tracer in average reflection light quantity and in terms ofthe width of spread of particles in the laminar flow region.

EXAMPLE 7

[0109] Using the spherical particles manufactured in Production Example1, namely a spherical particulate SiO₂ tracer with 70% of particleshaving diameters within the range of 2.5±0.7 μm (FIGS. 1 and 2) and thesame laser Doppler velocimeter as used in Example 1, the velocity ofwater flowing in a turbulent flow within a pipe of circular section wasdetermined and the relationship between sample data rate and meaneffective data rate was investigated. Thus, the flow rate was increasedstepwise to increase the number of data per unit time (sample data rate)and, hence, the quantity of particles passing through the fringe in thevelocimeter, with the concentration of particles being kept constant. Ofthe data thus generated, the percentage of the data useful for velocityassessment (effective data rate) was determined.

[0110] 1. Instrument: A fiber type laser Doppler velocimeter (FLDV)

[0111] (Ikeda, Y., Hikosaka, M., Ohira, T., and Nakajima, T., ScavengingFlow Measurements in a Fired Two-Stroke Engine by FLDV. 1991, SAE PaperNo. 910670.)

[0112] (Specification) Laser: He-Ne laser

[0113] Laser power: 8 mW×2

[0114] Lens diameter: 55 mm

[0115] 2. Measuring conditions:

[0116] Center frequency: 20 MHz

[0117] Band width: ±16 MHz

[0118] Effective sample number: 5,000

[0119] Signal gain: 24 dB

[0120] Photomultiplier voltage: 760 V

[0121] The results are shown in Table 5. TABLE 5 Sample data rate (Hz)Mean effective data rate (%) 1,000 72 2,000 69 3,000 70

COMPARATIVE EXAMPLE 6

[0122] Using the conventional particulate TiO₂ tracer with a meanparticle diameter of 2 μm (FIGS. 5 and 6), the velocimetric test wasperformed under the same conditions as used in Example 7. The resultsare shown in Table 6. TABLE 6 Sample data rate (Hz) Mean effective datarate (%) 1,000 35 2,000 20 3,000 10

COMPARATIVE EXAMPLE 7

[0123] Using the conventional particulate SiC tracer with a meanparticle diameter of 3 μm, the velocimetric test was performed under thesame conditions as in Example 7. The results are shown in Table 7. TABLE7 Sample data rate (Hz) Mean effective data rate (%) 1,000 50 2,000 423,000 37

[0124] It will be apparent from Tables 5 through 7 that, compared withthe tracers of Comparative Examples 6 and 7, the tracer of Example 7yields high effective data rates which are substantially constant up toa very high data rate.

EXAMPLES 8, 9 AND 10 AND COMPARATIVE EXAMPLES 8 AND 9

[0125] The five particulate tracers shown below in Table 8 wererespectively immersed in water for a predetermined time and the bulkspecific gravity of each wet tracer was determined. The results are alsoshown in Table 8. TABLE 8 Particulate tracer Bulk specific gravity[Example 8] 1.45 g/cm³ Porous spherical SiO₂ particles, closed pore 0.05cm³/g, mean particle diameter 2.7 μm [Example 9] 1.20 g/cm³ Porousspherical SiO₂ particles, closed pore 0.21 cm³/g, mean particle diameter2.8 μm [Example 10] 1.26 g/cm³ Porous spherical SiO₂ particles, closedpore 0.15 cm³/g, mean particle diameter 15 μm [Comparative Example 8] 2.3 g/cm³ Conventional SiC particles, mean particle diameter 3 μm[Comparative Example 9]  3.1 g/cm³ Conventional TiO₂ particles, meanparticle diameter 2 μm

[0126] It is apparent from Table 8 that compared with the tracers ofComparative Examples 8 and 9, the tracers of Examples 8, 9 and 10 aresmaller in the bulk specific gravity differential from water, suggestingthe greater ease with which they may follow a water flow and that thetracer of Example 9 is particularly excellent.

[0127] Since the fluid-tracking performance is inversely proportional tothe specific gravity differential from the fluid, the tracer of Example10 is considered to be substantially equivalent to the tracer ofComparative Example 8 in tracking efficiency. However, because thesectional area of the tracer particle of Example 10 is approximately25-fold greater, it is easy to anticipate that, in the photographingmethod, it produces a greater intensity of scattered light. The greaterthe intensity of scattered light, the higher is the measurementaccuracy. In other words, the smaller the specific gravity differentialfrom the fluid to be measured, the larger is the tracer particle thatcan be employed. Therefore, the fact that the tracer particle has closedpores and the specific gravity of the particle can be controlled bytaking advantage of such closed pores has a great significance in ameasuring system where the distribution of tracer particles isphotographed using an instantaneous powerful light source such as aflashlight or a pulse laser.

EXAMPLE 11

[0128] A velocimetric test was performed using a metal-clad sphericalparticulate tracer prepared by depositing a nickel plate about 0.05 μmthick on the particles manufactured in Production Example 1 by theelectroless plating technique. The test conditions were otherwiseidentical to those used in Example 7. The results are shown in Table 9.TABLE 9 Sample data rate (Hz) Mean effective data rate (%) 1,000 802,000 75 3,000 74

[0129] Comparison with Tables 5 through 7 and 9 indicates that theeffective data rates in Example 11 are higher than those obtained inExample 7 and Comparative Examples 6 and 7.

EXAMPLE 12

[0130] Using a porous hollow spherical particulate SiO₂ tracer with amean particle diameter of 1.5±S.D. 0.3 μm, the shell thickness of whichwas one-fifth of the diameter of the particle, a comparative feedingtest was performed with the measuring wheel particle feeder (MSF-F,Liquid Gas Co., Ltd.) and the screw feeder. In both cases, the feed ratewas set at 0.3 g per minute.

[0131] The feeding accuracy was high for both the measuring wheel feederand the screw feeder but with the measuring wheel feeder the tracercould be introduced with an accuracy of 0.3±0.01 g/min. This accuracy isabout 5 times as high as the accuracy with the screw feeder.

[0132] In the measurement of fluid velocity with a laser instrument, itis easy to see that the higher the accuracy with which the tracer can befed to the instrument and, hence, to the fluid to be measured, thehigher is the accuracy of flow measurement by the instrument.

COMPARATIVE EXAMPLE 10

[0133] Using the conventional non-agglomerating particulate SiO₂ tracerwith a mean particle diameter of 1.5 μm, a feeding test was performedwith the measuring wheel particle feeder and the screw feeder. In bothcases, the feed cate was controlled at 0.3 g per minute.

[0134] With the measuring wheel feeder, the tracer particles could notbe successfully delivered due to agglomeration.

[0135] The feed accuracy with the screw feeder was 0.3±0.14 g/min and itwas found that, compared with Example 12, the use of spherical tracerparticles insures a comparatively higher accuracy of feeding to thelaser instrument.

[0136] In the measurement of fluid flow with a laser instrument, it iseasy to see that the higher the accuracy of feed to the fluid, thehigher is the accuracy of measurement by the instrument.

EXAMPLE 13 AND COMPARATIVE Example 11

[0137] Using the conventional non-agglomerating particulate TiO₂ tracerwith a mean particle diameter of 5 μm, a feeding test was performed withthe same measuring wheel particle feeder as used in Example 12 (Example13) and the screw feeder (Comparative Example 11). In both cases, thefeed rate was set at 0.3 g per minute.

[0138] The feeding accuracies were 0.3±0.02 g/min and 0.3±0.08 g/min,respectively, indicating that the measuring wheel particle feeder isconductive to a higher measurement accuracy.

What is claimed is:
 1. A method of measuring the flow of a fluid usingan optical instrument and a porous particulate ceramic tracer whichcomprises employing a spherical particulate ceramic tracer having aparticle diameter within the range of 0.5 to 150 μm as said tracer.
 2. Amethod of measuring the flow of a fluid involving measuring the velocityof tracer particles with a laser instrument such as a laser Dopplervelocimeter, which comprises employing a spherical particulate tracerwith a particle diameter in the range of 0.5 to 10 μm as said tracer. 3.A method of measuring the flow of a fluid involving photographing of thedistribution of tracer particles with an instantaneous powerful lightsource such as a flashlight or a pulse laser, which comprises employinga spherical particulate ceramic tracer having a particle diameter withinthe range of 5 to 150 μm.
 4. A method of measuring the flow of a fluidaccording to any of claims 1 through 3 wherein said fluid to be measuredis a gas and said particulate tracer is a hollow spherical particulatetracer.
 5. A method of measuring the flow of a fluid according to any ofclaims 1 through 3 wherein said fluid to be measured is a liquid andsaid particulate tracer is a porous particulate ceramic tracer havingclosed pores with a porosity of not less than 0.1 cm³/g.
 6. A method ofmeasuring the flow of a fluid according to any of claims 1 through 3 and5 wherein said fluid to be measured is a liquid and said particulatetracer is a metal-clad ceramic tracer.
 7. A method of measuring the flowof a fluid according to claim 6 wherein said metal-clad tracer is atracer clad with a metal by electroless plating.
 8. a method ofmeasuring the flow of a fluid according to any of claims 6 and 7 whereinsaid metal is nickel.
 9. A method of measuring the flow of a fluidaccording to any of claims 1 through 8 wherein said particulate ceramictracer or the ceramic part of said metal-clad tracer is composed ofSiO₂.
 10. A method of measuring the flow of a fluid according to any ofclaims 1 through 9 wherein not less than 70% of particles constitutingsaid particulate ceramic tracer have diameters within the range of themean particle diameter±50%.
 11. A method of measuring the flow of afluid according to any of claims 1 through 10 wherein said particulateceramic tracer or the ceramic part of said metal-clad tracer has beenproduced by the reversed micelle process.
 12. A method of measuring theflow of a fluid according to claim 11 wherein said particulate ceramictracer or said ceramic part of said metal-clad ceramic tracer has beenproduced by extruding an aqueous solution of a precursor material forsaid tracer or ceramic part from a porous glass or polymer membranehaving pores substantially uniform in size into an organic solvent toform reversed micelles.
 13. A method of measuring the flow of a fluidaccording to any of claims 1 through 12 wherein said particulate ceramictracer is fed to said fluid by means of a measuring wheel particlefeeder.
 14. A method of measuring the flow of a fluid with a particulatetracer and an optical instrument such as a laser velocimeter whichcomprises feeding a non-agglomerating particulate tracer from ameasuring wheel particle feeder to the optical instrument.